退化高寒草甸关键生态属性对多途径恢复措施的响应特征

高寒草甸是青藏高原的主体植被类型,但退化态势较为严峻,严重威胁青藏高原生态屏障的战略地位。退化高寒草甸的复健是世界性难题,治理效果也因退化状态、恢复措施及气候环境而异。以春季休牧、秋季休牧、畜群结构优化、减畜轮牧、围栏封育及翻耕改建等典型多途径恢复措施下的退化高寒草甸为对象,系统探讨主要生态要素和生态功能的响应特征及潜在过程。结果表明,典型恢复措施下退化高寒草甸的植被生产力、土壤有机碳密度及土壤饱和持水量等生态要素都得到一定程度的提升,而恢复效果与实施年限及恢复措施密切相关。围栏封育和翻耕改建下土壤有机碳密度及饱和持水量随恢复年限均表现为对数饱和型的响应特征,退化高寒草甸固碳持水功能的基本恢复年限约为6—10年。春季休牧、秋季休牧、畜群结构优化、减畜轮牧、围栏封育等放牧管理恢复措施应适用于轻度退化至重度退化的高寒草甸,而翻耕改建则是极度退化高寒草甸的适宜治理措施。由于多途径恢复措施的关注目标不同,今后研究应集中在恢复措施的组合优化和综合评价等方面。

Responses of key ecological attributes to multi-path restoration measures of degraded alpine meadows

Alpine meadows are the key vegetation types of the Qinghai-Tibet Plateau and played critical roles in water-holding, carbon sequestration, and biodiversity conservations for China and Asian. Under the combinations of climate change and over-grazing practices, the alpine meadows have been widely experiencing degradation, which have seriously threatened the strategic status of the ecological barrier of the Plateau. Because of the frigid climate and fragile ecosystem, the rehabilitation of degraded alpine meadows has been a worldwide problem. And the restoration effects of degraded alpine meadow ecosystems also vary with the degraded gradations, restoration measures, and natural climatic conditions. The typical multi-path restoration measures such as grazing time management (spring rest-grazing and autumn rest-grazing), grazing intensity management (grazing livestock community optimization, rotation-reduction grazing, and fence enclosure) and tillage reconstructions were surveyed to explore the responses of key ecological variables and their underlying ecological processes of the degraded alpine meadows. The results showed that aboveground biomass, belowground biomass, soil organic carbon, and soil saturated water contents of degraded alpine meadows were clearly promoted under the multi-path restoration measures. The restoration effects varied with treatment durations and specific measures. Comparing with autumn rest-grazing, spring rest-grazing could be a better option of grazing time management for lightly and heavily degraded alpine meadows. The ecological functions of soil carbon sequestration and water holding capacity under fence enclosure and tillage reconstruction showed a positive but saturating logarithmic relationship with treatment durations. And their appropriate durations in ecological restoration of the degraded meadows was about 6-10 years. For heavily degraded alpine meadows, the fence enclosure should be first adopted for 6-10 years and then grazing livestock community optimization and rotation-reduction grazing could be later used for the balance between ecological function and stockbreeding development. Therefore, the restoration measures of grazing time and intensity management should be mainly applied to alpine meadows with lightly and heavily degradation. As for extremely degraded alpine meadows, generally referred to as "black soil beach", the tillage reconstruction would be an appropriate measure. Soil carbon sequestration and water holding capacity was significantly promoted after 6-year tillage planting treatment. Due to the different initial targets of multi-path restoration measures, future researches should focus on the scientific combinations and comprehensive assessments of restoration measures. Those countermeasures should take the restoration staff and time costs and ecological rehabilitation efforts into full considerations and balance the function of ecology, production, and livelihood of alpine meadow ecosystems.